Upgrade from PXC 5.5 to 5.6 failed

After installing PXC 5.6 and want to start the node, an error occured:

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2014-02-15 21:15:47 22747 [Note] Server socket created on IP: '::'.
13:15:47 UTC - mysqld got signal 11 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
We will try our best to scrape up some info that will hopefully help
diagnose the problem, but since we have already crashed,
something is definitely wrong and this may fail.
Please help us make Percona XtraDB Cluster better by reporting any
bugs at https://bugs.launchpad.net/percona-xtradb-cluster

key_buffer_size=67108864
read_buffer_size=2097152
max_used_connections=0
max_threads=4098
thread_count=0
connection_count=0
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 42090478 K bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x12981410
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 7fffc542b500 thread_stack 0x20000
/usr/sbin/mysqld(my_print_stacktrace+0x2e)[0x8ecfde]
/usr/sbin/mysqld(handle_fatal_signal+0x4a1)[0x6b79b1]
/lib/x86_64-linux-gnu/libpthread.so.0(+0xf030)[0x7fa358e3c030]
/usr/sbin/mysqld(_Z9get_fieldP11st_mem_rootP5Field+0x52)[0x7a2db2]
/usr/sbin/mysqld(_Z10acl_reloadP3THD+0x101b)[0x6d6a0b]
/usr/sbin/mysqld(_Z8acl_initb+0x161)[0x6d8ee1]
/usr/sbin/mysqld(_Z11mysqld_mainiPPc+0xb56)[0x5ff826]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xfd)[0x7fa357485ead]
/usr/sbin/mysqld[0x5f2c0d]

Trying to get some variables.
Some pointers may be invalid and cause the dump to abort.
Query (0): is an invalid pointer

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my.cnf is in attachment

Is there anything I missed, or something should be provided for further?

Comment

Stephon - did you get this upgrade working? We're about to take the 5.6.15 plunge, on Ubuntu 12.04. Any tips you can offer?
We already have noted that wsrep_incoming addresses are blank. A Percona engineer also advised us to be wary of this bug.